This application relates to a display device and a method for manufacturing a display device. More specifically, the application relates to a method for manufacturing a self-luminous display device employing an organic electro luminescence (EL) element.
In recent years, the organic EL display employing the organic EL element is attracting attention as a display device to replace the liquid crystal display. The organic EL display is a self-luminous display in which an organic material itself emits light in response to current application to the material. The organic EL display has the following excellent features: no necessity for a backlight, excellent color reproducibility, high contrast, responsiveness suitable for a moving image, a wide viewing angle, etc.
Meanwhile, the organic EL display involves the deterioration of the organic layer of the organic EL element due to moisture absorption, and thus has e.g. problems that the emission luminance of the organic EL element is lowered and that the light emission becomes unstable.
For the organic EL display, there has been proposed an active-matrix system in which a thin film transistor (TFT) is disposed as a switching element for each pixel and the organic EL element included in the pixel is controlled.
In the organic EL display of this active-matrix system, an organic insulating film having a flat surface is formed as a layer located above the TFT, and plural organic EL elements are formed into a matrix on the flat surface of this organic insulating film. This organic insulating film has water-permeable nature. If water is diffused into a display area P in which the organic EL elements are disposed due to this organic insulating film, the organic EL elements are deteriorated and problems of displaying failure and so forth occur.
Various techniques to prevent the diffusion of water into the display area P have been proposed. For example, Japanese Patent Laid-open No. 2006-054111 (hereinafter, Patent Document 1) proposes a technique of providing a separator surrounding the display area. In this technique, by the separator, water remaining in the peripheral area can be prevented from entering the display area. For example, Japanese Patent Laid-open No. 2005-266667 (hereinafter, Patent Document 2) proposes a technique of providing pores reaching the first insulating film in the lower electrode disposed in the peripheral area to thereby discharge water and so forth included in the first insulating film.
In an organic EL display having a top-emission structure, in which light is extracted from the sealing panel side, the electrode of the light-extraction side (upper electrode) is an electrode common to the respective organic EL elements and is formed by using an optically-transmissive, electrically-conductive material such as indium tin oxide (ITO).
However, the resistivity of such an optically-transmissive, electrically-conductive material is higher by about two or three orders of magnitude than that of a normal metal material. Thus, the voltage applied to the upper electrode is uneven in the plane, which leads to a problem that variation in the emission luminance from position to position arises among the respective organic EL elements and the displaying quality is lowered.
To address this problem, e.g. Japanese Patent Laid-open No. 2004-207217 (hereinafter, Patent Document 3) proposes a technique of forming a power supply auxiliary interconnect for being connected to the cathode electrode in the same layer as that of the anode electrode. In this technique, the power supply auxiliary interconnect in the same layer as that of the first electrode is connected outside the display area, and the cathode electrode and the power supply auxiliary interconnect are connected also in the display area. Thereby, the cathode voltage is stabilized.
In the technique of Patent Document 3, an AlNd alloy is used as the anode electrode material in order to ensure high reflectance of the anode electrode, whereas an optically-transmissive MgAg alloy is used for the cathode electrode. However, a natural oxide film is easily generated on the surface of the AlNd alloy. This increases the contact resistance between the cathode electrode and the power supply auxiliary interconnect, which is composed of the same material as that of the anode electrode, and thus causes a problem that the connection between the cathode electrode and the power supply auxiliary interconnect becomes electrically unstable.
To address this problem, e.g. PCT Patent Publication No. WO2007/148540 brochure (hereinafter, Patent Document 4) proposes a technique in which the cathode electrode is brought into contact with a Ti/Al/Ti multilayer film as the second metal layer forming the signal line and the power supply line of the circuit formed by using a TFT and the cathode electrode is connected to an AlNd alloy as the auxiliary interconnect via Ti.
Specifically, in this technique, as shown in FIG. 28, a contact pad 225 formed of the Ti/Al/Ti multilayer film is electrically connected to an auxiliary interconnect 214 composed of the AlNd alloy. Furthermore, a cathode electrode 218 composed of an MgAg alloy is electrically connected to the contact pad 225. Thereby, the auxiliary interconnect 214 and the cathode electrode 218 are electrically connected to each other via the contact pad 225.
To form this connection structure, an aperture for leading the auxiliary interconnect 214 to a lower layer is formed in a planarization insulating film 213. In an aperture-defining insulating film 216, an aperture for leading the cathode electrode 218 to a lower layer is formed. Furthermore, in order to prevent the cathode electrode 218 formed along the inner wall surface of this aperture from being broken due to steps, the size of the aperture by the aperture-defining insulating film 216 is set larger than the size of the aperture by the planarization insulating film 213. Thus, the flat surface of the planarization insulating film 213 partially has an exposed surface that is not covered by the aperture-defining insulating film 216. The cathode electrode 218 is formed along this exposed surface and the inner wall surface of the aperture by the planarization insulating film 213.
As the material of the aperture-defining insulating film 216 and the planarization insulating film 213, a photosensitive resin such as polybenzoxazole or polyimide is used as described in Japanese Patent Laid-open No. 2002-116715 (hereinafter, Patent Document 5) and Japanese Patent Laid-open No. 2001-160486 (hereinafter, Patent Document 6) for example. After this photosensitive resin is applied, the aperture-forming part is exposed and the exposed part is removed by a removing liquid. Thereby, the aperture by the aperture-defining insulating film 216 and the aperture by the planarization insulating film 213 are formed.